Several double effect absorption refrigerating systems are known wherein a heated refrigerating medium is utilized to heat water or the like for several purposes in parallel with the refrigerating cycle.
For example, there are several U.S. Patents relating to double effect refrigeration such as U.S. Pat. Nos. 3,605,432; 3,651,654; 3,292,385; 3,530,684; and 3,266,266. However, in each of the systems disclosed in these prior art publications, heat energy in a refrigerant discharged from a low pressure generator or a second generator was lost or was discharged without being used by merely passing the vaporized refrigerant or liquid refrigerant carrying heat energy through a liquid sealing portion or trap into a cooling medium or water thereby wasting the heat energy without utilizing such energy to improve the efficiency of the refrigerating cycle. Also, the refrigerant used to effect heat transfer in the low pressure generator is generally passed through a pressure reduction means, such as a float valve or a throttle orifice, before being fed to a condenser. However, a gas-bypassing (vapor accompanied by liquid to be delivered) is transitionarily experienced where a float valve is used and it is also inevitable when a orifice is operated under conditions other than design conditions. Such passing of the refrigerant vapor also results in a great loss in heat energy since it retains a relatively large amount of heat energy.
Also, Japanese Pat. No. 647,515 issued to Hitachi Ltd. is prior art in this field; however, this is intended to avoid the problem of crystallization in a double effect absorption type refrigerator and to enlarge the available range of the concentration of the solution in the high pressure generator by parallely flowing the solution to a high pressure generator and a low pressure generator and returning the refrigerant to an absorber and there is no teaching of utilizing the wasted heat energy as discussed above.
Therefore, it is desirable to prevent such waste of heat energy thereby lowering the operating cost and improving the efficiency of the refrigeration cycle.
To such end, in the U.S. application Ser. No. 752,661 filed by the same inventors as those in this application, now U.S. Pat. 4,085,595, closed a novel system wherein the refrigerant passed through the low pressure generator and still carrying heat energy was intentionally directed to a heat exchanger where the remaining heat energy in the refrigerant was transferred to part of a weak solution bypassed from a feed line between a high level heat exchanger and a low level heat exchanger so as to utilize the heat energy heretofore wasted.
The system disclosed in the U.S. application referred to above satisfactorily increases the efficiency of the system. However, in that system, the solution discharged from a high pressure generator and introduced into the low pressure generator is utilized to heat the weak solution before its introduction into the high pressure generator at the high level heat exchanger located upstream of the high pressure generator and therefore it is cooled before being introduced into the low pressure generator. The solution is concentrated in the high pressure generator and, thus, that solution becomes stronger if it is cooled in the high level heat exchanger. Assuming that the respective temperatures of the condensed solution discharged from the high pressure generator and the weak solution which is bypassed as above are approximately the same, the ability of the concentrated solution to absorb heat is naturally higher and, thus, the capacity of the low pressure generator is affected more by the concentrated solution than the bypassed solution. Therefore, it is preferable, in order to further improve the efficiency of the low pressure generator or the whole system, to raise the temperature of the cooled concentrated solution rather than raising the temperature of the bypassed weak solution to be introduced into the low pressure generator. Also, if the return line of the concentrated solution directed to the low pressure generator is arranged to pass through an additional heat exchanger where heat exchange is effected between the concentrated solution and the refrigerant passed through the low pressure generator, it makes possible the designing of a construction incorporating such additional heat exchanger in the low pressure generator thereby making the whole system more compact.